The preferred embodiment concerns a method to determine the concentration of toner particles in a carrier fluid in a liquid developer system for printers or copiers. The invention also concerns a measurement chamber to determine the concentration of toner particles in a carrier fluid.
In printers and copiers, a liquid developer system which contains a suspension made up of carrier fluid and toner particles is frequently used to ink a latent image on an intermediate carrier. These toner particles then gave the image the necessary color, for example black, monochrome or color mixtures. The concentration of toner particles in the carrier fluid fluctuates depending on different environmental conditions, for example depending on the evaporation of the carrier fluid as a result of temperature fluctuations and/or humidity fluctuations, and in particular depending on the proportion of ink per printed page. This concentration of toner particles can consequently be higher or lower than a desired operating value. Without countermeasures, a change of the concentration produces a variation of the fluidity of the liquid developer, and therefore a variation of its ability to be processed. Moreover, the mobility of the electrically charged toner particles which are exposed to an external electrical field can vary, whereby the quality of the inking of the latent image on the intermediate carrier is negatively affected. Moreover, the inking of the latent image is dependent on the concentration of the toner particles. It is therefore necessary to keep the current concentration of toner particles at a constant optimal operating value over the operating time during the operation of the printer or copier. For this a regulation process is generally used, wherein it is necessary to continually establish the concentration of toner particles in the carrier fluid.
From Patent Abstracts of Japan JP 03146356 A it is known to keep the concentration of toner particles uniformly constant during the coating process. For this a detector detects the electrical resistance between two electrodes that are submerged in the suspension of carrier fluid and toner particles.
A liquid developer method in which toner particles jump over onto charged paper and thereby mask the paper charge is known from Patent Abstracts of Japan JP 03153278 A. After the development, the paper charge is a measure of the completeness of the development process, and indirectly a measurement for the toner concentration.
A measurement method to measure the toner concentration in which a toner image on the photoconductor is subjected to an optical reflection measurement is known from Patent Abstracts of Japan JP 10268645 A. The concentration of the toner is concluded from the measurement result. A similar method is also described in JP 11065295 A.
From Patent Abstracts of Japan JP 2000146827 A and JP 2001042652 A it is known to determine the concentration of toner particles with the aid of an optical sensor that evaluates the transmission.
From Patent Abstracts of Japan JP 2003186309 A it is known for a liquid developer system to determine the toner concentration via reflection measurement with the aid of an optical reflex sensor.
From U.S. Pat. No. 5,121,629 A it is known to determine the concentration of particles in a suspension with the aid of an ultrasound sensor. Ultrasound waves with selected, discrete frequencies across a selected frequency range are directed towards the suspension, and the attenuation of the amplitudes of the ultrasound waves upon penetration of the suspension are measured.
A method and a device in which ultrasound sensors are used to measure the concentration of solid particles in a suspension is known from DE 199 44 047 C2. Ultrasound waves are conducted through the suspension on at least two different sound paths. The absorption of ultrasound in the suspension is determined, and the concentration of the particles is determined from this.
A method to determine drinking water consumption by means of ultrasonic measurement is known from WO 2006/021266 A1. A measurement signal is thereby emitted that is derived from a clock signal. A capacitor is charged after the received signal has exceeded a reference value after a wait time and a rising edge of the clock signal appears. The charging of the capacitor is ended as soon as a rising edge of the output signal appears. The charge time together with the wait time yields the total measurement time. The water consumption is determined from the measurement time. The method is applied to a clear liquid in which the attenuation of the received oscillation is comparably low.
A measurement chamber to measure a solid concentration by means of ultrasound is known from DE 10 2007 025 251 A1. An emitter emits an ultrasonic wave at an emulsion of carrier fluid and toner particles. The emulsion is thereby pumped through the measurement chamber. The receiver receives the ultrasonic wave. The measurement chamber is thereby arranged horizontally so that the fluid flows through the measurement chamber in the horizontal direction. If the fluid does not flow, solid particles can deposit on the floor (and thus on the receiver), whereby the measurement result is adulterated.
Optical detection methods have the disadvantage that they are imprecise given strongly absorbent carrier fluids. Moreover, gas bubbles in the suspension can significantly adulterate the measurement. Electrical sensors that evaluate the conductivity of the suspension to determine the concentration are likewise relatively imprecise since the conductivity properties can change significantly during the operation of the printer or copier. Moreover, toner particles can adhere to the electrodes, which adulterates the measurement result.